jwalit patel

7/31/2019 Jwalit Patel

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INTRODUCTION

CIRCUIT & MODEL

OPERATING MECHANISM

ARC PHENOMENA

ADVANTAGES

DISADVANTAGES

APLICATIONS


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SWITCH GEAR:

The term switchgear, used in association with the electric power system, or

grid, refers to the combination of electrical disconnects, fuses and/or circuitbreakers used to isolate electrical equipment.

SWITCHGEAR EQUIPMENT:

FuseCircuit breakerIsolatorEar thing switchLightening arresterCurrent transformerPotential transformer
http://en.wikipedia.org/wiki/Fuse_(electrical)http://en.wikipedia.org/wiki/Circuit_breakerhttp://en.wikipedia.org/wiki/Circuit_breakerhttp://en.wikipedia.org/wiki/Circuit_breakerhttp://en.wikipedia.org/wiki/Circuit_breakerhttp://en.wikipedia.org/wiki/Fuse_(electrical)


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CIRCUIT BREAKER:

Circuit breakers are mechanical devices designed to close or open contactmembers, thus closing or opening of an electrical circuit under normal orabnormal conditions.

TYPES OF CIRCUIT BREAKER:

AIR BLAST CIRCUIT BREAKEROIL CIRCUIT BREAKERSF6(SULPHUR HEXACHLORIDE) CIRCUIT BREAKERD.C. CIRCUIT BREAKERAIR BREAK CIRCUIT BREAKER


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AIR BLAST CIRCUIT BREAKER:

In air blast circuit breakers, compressed air at a pressure of 20-30 kg/cm*cm isemployed as an arc quenching medium.

Air blast circuit breakers are suitable for operating voltages of 132 kV andabove. They have also been used in 11kV-33kV range for certain applications.

HISTORY:

An early form of circuit breaker was described by Thomas Alva Edison in an1879 patent application, although his commercial power distribution systemused fuses.

Its purpose was to protect lighting circuit wiring from accidental short-circuits

and overloads.
http://en.wikipedia.org/wiki/Thomas_Alva_Edisonhttp://en.wikipedia.org/wiki/Thomas_Alva_Edison


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DETAIL OF AIR BLAST CIRCUIT BREAKER:

It also called as compressed aircircuit breaker.

Gases such as nitrogen, carbondioxide, hydrogen or Freon can

be used as arc interruptingmedium. But compressed air isthe most accepted arcinterrupting medium.

Carbon dioxide has a draw backas it is difficult to control owing tofreezing at valves and otherrestricted passages. Hydrogenhas increased breaking capacitybut its costlier.


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High-pressure air,(about 20-30atm.) is stored in the reservoir.Air is taken from the compressedair system.

Three hollow insulator columnsare mounted on the top of hollowinsulator chambers.

The current carrying parts connectthe three arc extinction chambersto each in series and the pole tothe neighboring equipment.

Since there exist a very highvoltage between the conductorand the air reservoir, the entire arcextinction chamber assembly ismounted on insulator.


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When a electrical signal is actuated the operating mechanism operatesthe rod and valves are made open to send the high pressure air in thehollow insulator

The high pressure rapidly enters the double arc extinction chamber .

As the air enter the arc extinction chamber the pressure on the movingcontact become more than spring pressure and make the contactsopen.The contact travel through a short distance against the spring pressure.

At the end of contact travel the port for outgoing air is closed by themoving contact and the entire arc extinction chamber is filled with highpressure air, as the is not allowed to go out.

However during the arcing the air goes out through the opening andtakes away the ionized particles of arc.


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CROSS BLAST CIRCUIT BREAKER

In this a high pressure blast of air isdirected perpendicular to the arc for itsinterruption.

The arc is forced into a suitable chute.Sufficient lengthening of arc is obtained,resulting in the introduction ofappreciable resistance in the arc itself.

Therefore, resistance switching is notcommon in this type of circuit breakers.

This are suitable for interrupting highcurrent at comparatively lower voltages.

TYPE OF ABCB:


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AXIAL BLAST CIRCUIT BREAKERSINGLE BLAST TYPEDOUBLE BLAST TYPE

In this a high pressure blast of air is directedlongitudinally(in line with the arc).

Axial blast circuit breaker are suitable for extrahigh voltage and super high voltageapplication.

This because interrupting chambers can befully enclosed in porcelain tubes.Resistance switching is employed to reducethe transient over voltages.

The number of breaks depends upon thesystem voltage, for example, 4 at 220 kV and 8at 750 kV.

Air blast circuit breaker have also beencommissioned for 1100 kV system.


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An arc is struck whencontacts are separated, thecurrent is thus able tocontinue.

Thus the main duty of circuitbreaker is to distinguish thearc within the shortestpossible time.

The arc provides the lowresistance path to the currentand the current in the circuitremains uninterrupted.


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When fault occurs current flow through contacts before they are being

separated.

At the instant when contact separates, the contact area decreases andthe large fault current cause increased current density and hence rise intemperature occur due to which the surrounding air or oil get ionized.

They acts as conductor and an arc is struck between them.

The potential difference between contacts is sufficient to maintain the arc.

The arc provides a low resistance path and current flows till the arcpersists. The current flow depends on the arc resistance. As theresistance increases current flow between the contacts decreases.


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Arc resistance depends on:

Degree of ionizationarc resistance increases with decrease in number of ionized particles.Length of arcarc resistance increases with length of the arc i.e. separation of contacts.Cross-section of arc

arc resistance increases with decrease in the area of x-section of thearc.

Arc interruption

Circuit breakers are usually able to terminate all current very quickly:typically the arc is extinguished between 30 ms and 150 ms after themechanism has been tripped, depending upon age and construction of thedevice.


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In air blast circuit breaker ,thearcing products are completelyremoved by the blast.

There is no regular expense of oil

replacement.

Due to lesser arc energy, air blastcircuit breakers are very suitablefor conditions where frequent

operation is required.

It mostly does not have anyleakage problem.

In oil circuit breaker, the oildeteriorates with successiveoperation.

There is regular expense of

oil replacement after someperiod.

It has comparatively higher arcenergy, so not used where

frequent operation is required.

It may have problem of oilleakage.


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AIR BLAST

CIRCUIT

BREAKER

OIL CIRCUIT

BREAKER


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OIL CIRCUIT BREAKER


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The risk of fire is eliminated.

The arcing products are completely removed by the blast where the oildeteriorates with successive operations,the expense of regular oil is replacement is avoided.

The growth of dielectric strength is so rapid that final contact gap needed

for arc extinction is very small. This reduces the size of device.

The arcing time is very small due to the rapid build up of dielectricstrength between contacts. Therefore, the arc energy is only a fraction thatin oil circuit breakers, thus resulting in less burning of contacts.

Due to lesser arc energy, air blast circuit breakers are very suitable forconditions where frequent operation is required.

The energy supplied for arc extinction is obtained from high pressure air

and is independent of the current to be interrupted.


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Air has relatively inferior arc extinguishing properties.

Air blast circuit breakers are very sensitive to the variations in the rateof restriking voltage.

considerable maintenance is required for the compressor plant which

supplies the air blast.

Arc furnace duty Traction system

Air blast circuit breakers are finding wide applications in high voltageinstallations.

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